The present invention relates to a photodetecting system for a surveying instrument equipped with an automatic tracking device and, more particularly, to a photodetecting system for a surveying instrument, capable of controlling the collimation of the surveying instrument by simple photodetecting means.
There are surveying instruments provided with an automatic tracking device. An automatic surveying instrument disclosed in Japanese Patent Laid-open No. Hei 5-322569 is capable of tracking an object to measure the position of the object and comprises encoders for electrically measuring horizontal angle and vertical angle, a range finer, a collimator and a tracking device. A body is driven for turning in a horizontal plane by a motor, and the collimator is turned in a vertical plane by a motor.
The collimator emits distance measuring light for measuring the distance between the surveying instrument and the object, and tracking light for tracking the object. The object is provided with a reflecting prism for reflecting the distance measuring light and the tracking light.
In the known automatic surveying instrument, however, the intensity of the tracking light, as well as that of the distance measuring light, is limited by the overall size of the automatic surveying instrument and necessity for securing safety, and a substantially collimated beam of light must be moved at a high speed for scanning in a range to track and detect a long-distance object.
The high-speed scanning needs a high-speed scanning means, such as an acoustooptic device or a galvanometer mirror, to realize high-speed scanning. Consequently, the construction of the automatic surveying instrument becomes complicated, the body becomes large and power consumption increases inevitably. A laser beam must be moved vertically and horizontally for high-speed scanning by a high-speed scanning means, such as a galvanometer mirror or the like, the automatic surveying instrument has very complicated construction and is expensive and uneconomical.
Another tracking method may use image processing instead of high-speed scanning. A scanning method using image processing processes an image taken by a television camera mounted on a telescope to extract a reflecting prism position and direct the surveying instrument toward a collimation center. However, although there is no structural difficulty in mounting the television camera on the surveying instrument, the tracking method using image processing needs a large-scale, complicated electric circuit for image processing. Such an electric circuit is difficult to build in the surveying instrument, consumes much power and needs an external power supply.
The present invention provides a photodetecting system for a surveying instrument, capable of controlling the collimation of the surveying instrument by simple photodetecting means. A collimating optical system collimates a telescope toward an object, a splitting optical device splits incident light received from the collimating optical system and directs split beams of light toward a first photodetector and a second photodetector, a first condensing device disposed on an optical axis between the first photodetector and the splitting optical device gathers light in a first direction, a second condensing device disposed on an optical axis between the second photodetector and the splitting optical system gathers light in a second direction perpendicular to the first direction.